Determining composition of a sample

ABSTRACT

A single-wavelength light source is configured to generate an excitation light source. A sample holder that defines an inner cavity is capable of holding a sample and includes a surface transparent to the excitation light source. One or more mounts are attached to at least one of the light source or the sample holder. The mounts are configured to change an incident angle of the excitation light source on the surface. One or more optical components are positioned in a path of a fluorescence emission emitted from the surface and guide the fluorescence emission to a detector. A detector detects an intensity of the fluorescence emission.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of priorityto U.S. patent application Ser. No. 15/681,940, filed Aug. 21, 2017, nowU.S. Pat. No. 10,845,306, the contents of which are hereby incorporatedby reference.

TECHNICAL FIELD

This disclosure relates to fluid fluorescence.

BACKGROUND

Some fluids can fluoresce, that is, they give off light when stimulatedby a certain wavelength of light from an external source. Differentfluids are sensitive to different wavelengths of light and differentfluids fluoresce different wavelengths of light when stimulated orexcited.

SUMMARY

This disclosure relates to determining a composition of a sample.

An example implementation of the subject matter described within thisdisclosure is a fluorescence-measurement apparatus with the followingfeatures. A single-wavelength light source is configured to generate anexcitation light source. A sample holder that defines an inner cavity iscapable of holding a sample and includes a surface transparent to theexcitation light source. One or more mounts are attached to at least oneof the light source or the sample holder. The mounts are configured tochange an incident angle of the excitation light source on the surface.One or more optical components are positioned in a path of afluorescence emission emitted from the surface and guide thefluorescence emission to a detector. A detector detects an intensity ofthe fluorescence emission.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The one or more mounts includes a rotatable mount attached to a base ofthe sample holder and can rotate the surface of the sample holder inrelation to the excitation light source.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.An axis of rotation of the sample holder is positioned verticallythrough the center of the sample holder.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.An axis of rotation of the sample holder is positioned verticallythrough the center of the surface of the sample holder.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The surface is tilted relative to a vertical axis in range from 0°-80°.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The light source includes a laser in an ultraviolet spectrum at adefined wavelength.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The detector includes a monochromator coupled to a photomultiplier.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following. Afilter is positioned between the surface and the detector and isconfigured to pass a specified range of wavelengths and filter outwavelengths different from the specified range.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The one or more optical components can include a lens positioned betweenthe surface and the detector that is configured to focus thefluorescence emission on an inlet of a fiber optic cable. A fiber opticcable can be positioned between the lens and the detector with the inletconfigured to receive the focused fluorescence emission and an outletpositioned to direct the focused fluorescence emission to the detector.

Aspects of the example implementation, which can be combined with theexample implementation alone or in combination, include the following.The sample can include a hydrocarbon fluid.

An example of the subject matter described within this disclosure is amethod with the following features. A fluid sample is received by asample holder defining an inner cavity capable of holding a sample andthat includes a surface that is transparent to an excitation lightsource. Fluorescence is induced in the fluid sample by a light producedby a single-wavelength light source. An angle of incidence between thesurface of the sample holder and the light is changed. A change influorescence intensity is detected by a detector as the angle ofincidence is changed.

Aspects of the example method, which can be combined with the exampleimplementation alone or in combination, include the following. A plot offluorescence intensity vs. the angle of incidence is plotted. The plotis compared to a library of plots. A content of the fluid sample isdetermined in response to comparing the plot.

Aspects of the example method, which can be combined with the exampleimplementation alone or in combination, include the following. Changingthe angle of incidence includes rotating the sample holder.

Aspects of the example method, which can be combined with the exampleimplementation alone or in combination, include the following. Rotatingthe sample holder can include rotating the sample holder about an axisof rotation of the sample holder that is positioned vertically throughthe center of the sample holder.

Aspects of the example method, which can be combined with the exampleimplementation alone or in combination, include the following. Rotatingthe sample holder can include rotating the sample holder about an axisof rotation of the sample holder that is positioned vertically throughthe center of a face of the sample holder.

Aspects of the example method, which can be combined with the exampleimplementation alone or in combination, include the following. Changingan angle of incidence is controlled by a microprocessor.

Aspects of the example method, which can be combined with the exampleimplementation alone or in combination, include the following. The fluidsample includes hydrocarbon fluid.

Aspects of the example method, which can be combined with the exampleimplementation alone or in combination, include the following. Changingthe angle of incidence includes varying the angle between 0°-80°.

An example implementation of the subject matter described within thisdisclosure is a fluid identification system with the following features.A sample holder is filled with an unknown fluid. The sample holder istransparent to a specified wavelength of light. A laser is capable ofdirecting a laser beam towards a face of the sample holder. A detectoris directed towards the face of the sample holder. The detector iscapable of detecting florescent emissions from the unknown fluid withinthe sample holder. a microprocessor is also included. Acomputer-readable storage medium stores instructions that are executableby the microprocessor. The instructions include emitting a laser beamfrom a laser at the face of the sample holder, inducing fluorescence inthe fluid by the laser beam produced by a laser at a specifiedwavelength, changing an angle of incidence between the face of thesample holder and the laser beam, detecting a change in fluorescenceintensity as the angle of incidence is changed, plotting a plot offluorescence intensity vs. the angle of incidence, comparing the plot toa library of plots, and determining a composition of the fluid inresponse to comparing the plot.

Aspects of the example system, which can be combines with the exampleimplementation alone or in combination, include the following. Theunknown fluid includes a hydrocarbon fluid.

Aspects of the example system, which can be combines with the exampleimplementation alone or in combination, include the following. Rotatingthe sample holder includes rotating the sample holder about an axis ofrotation of the sample holder that is positioned vertically through thecenter of the sample holder.

Aspects of the example system, which can be combines with the exampleimplementation alone or in combination, include the following. Rotatingthe sample holder comprises rotating the sample holder about an axis ofrotation of the sample holder that is positioned vertically through thecenter of a surface of the sample holder.

The details of one or more implementations of the subject matterdescribed in this disclosure are set forth in the accompanying drawingsand the description below. Other features, aspects, and advantages ofthe subject matter will become apparent from the description, thedrawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example fluorescence-measurementapparatus.

FIGS. 2A-2B are schematic diagrams showing a side cross sectional viewof a sample holder containing a sample.

FIGS. 3A-3B are schematic diagrams showing perspective views ofrotatable sample holder mounts.

FIGS. 4A-4B are schematic diagrams showing top-down views of rotatablesample holder mounts.

FIG. 5 is a schematic diagram showing a light source for thefluorescence-measurement apparatus.

FIGS. 6A-6D are example plots of fluorescent intensities for differentpotential samples.

FIG. 7 is a flowchart of an example method for identifying a sampleusing fluorescent intensities.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

At remote work sites and facilities, such as an off-shore production ordrilling platform, technicians can be asked to identify unknownsubstances. The reasons for identification can include checking forcontamination, verifying a mixture ratio, determining a substance in anunlabeled container, or other reasons. Many identification tests ofsample are typically sent off-site to a lab and can have a turn-aroundtime of several days or longer. In many instances, it is preferable foran on-site technician to be able to identify the substance quickly andon-site.

This disclosure describes a method and apparatus for identifying fluidsbased on fluorescence of the fluids. The apparatus can include anexcitation light source for inducing fluorescence in a sample, a sampleholder for holding the sample, and a photodetector to measure theintensity of the fluorescence. The excitation light beam can be directedat the sample at a non-perpendicular angle to a flat, transparentsurface of the sample holder. The laser can induce an inner-filtereffect in the fluid due to a depth of penetration of the laser beam intothe fluid. The detector detects the fluorescence intensity of theinner-filter effect is detected and the detector can be configured todetect the wavelength of the expected fluorescence. A beam dump maycapture the light reflected off of the face of the sample holder toprevent or otherwise reduce interference with the detected fluorescence.In some implementations, the sample holder is rotated in order to vary adepth of penetration of the light beam into the fluid, and consequentlythe fluorescent intensity of the inner-filter effect can vary. In someimplementations, the sample holder is held stationary and the laser ismoved to different positions to vary a depth of penetration of the laserbeam into the sample (such as fluid), and consequently the fluorescentintensity of the inner-filter effect can vary. The intensity variationsare recorded against the angle of incidence between the laser and thefront of the sample holder. The plot produced from this test can be usedto identify the fluid.

FIG. 1 shows a fluorescence-measurement apparatus 100 in accordance withsome implementations of the present disclosure. For example, thefluorescence-measurement apparatus 100 can be configured to measurevariations in fluorescent intensities based on incident angles of anexcitation light. At a high level, the apparatus 100 includes a sampleholder 102, an excitation light source 104 configured to directexcitation light on the sample hold 102, and a detector 112 configuredto detect fluorescent intensity in response to the excitation light. Byplotting the fluorescent intensity as a function of incident angle, theapparatus 100 can, in some implementations, identify a sample containedin the sample holder 102.

The sample holder 102 that defines an inner cavity capable of holding asample, such as a fluid. The sample holder 102 includes a surface thatis transparent to an excitation light source 104. The sample holder 102can be a quartz cuvette, a glass sample container, or any other samplecontainer with a flat surface that is transparent to the specifiedwavelengths of the light source 104. In some implementations, only asingle side of the sample holder is transparent to the specifiedwavelengths of the light source 104.

The excitation light source 104 emits a beam 106 of a single wavelengthof light that is capable of generating fluorescence in a sample. In someimplementations, the excitation light source 104 emits a beam 106 oflight containing multiple wavelengths with at least one wavelength thatis capable of generating fluorescence in the sample. In someimplementations, the light source 104 can be a laser that emits a laserbeam at a defined wavelength, for example, in an ultraviolet wavelength.In some implementations, the wavelength of the light beam 106 can bebetween 266 nanometers and 355 nanometers. The light source can have apower output between twenty and fifty milliwatts. In someimplementations, the sample can fluoresce after one second of exposureto the light beam 106. The light source can emit either a continuous orpulsed light beam.

In order to change the incident angle of the excitation light, theapparatus 100 can also include one or more mounts attached to either thelight source 104, the sample holder 102, or both. The mounts can beconfigured to change an incident angle of the beam 106 relative to thesurface of the sample holder 102. For example, the mount can move thelight source 104 in a circular path around the sample holder 102. Insome implementations, the incident angle can range from 0°-80°. Theangle of incidence can be changed continuously or in steps. For example,5° steps can be taken between measurements.

The apparatus 100 can also include one or more optical components 108positioned between the sample holder 102 and the detector 112. Forexample, the one or more optical components are position in a path offluorescence emission 110 emitted from the surface of the sample holder102. In the instances, the one or more optical components 108 areconfigured guide or otherwise pass the fluorescence emission 110 to thedetector 112. As illustrated, the one or more optical components 108includes a filter 118 positioned between the surface of the sampleholder 102 and the detector 112. The filter 118 can pass a specifiedrange of wavelengths and filter out or otherwise block wavelengthsdifferent from the specified range. The filter 118 can be a notch filteror any other optical filter. The optical components 108 can also includea lens 120 positioned between the filter 118 and a fiber optic cable122. The lens 120 is configured to focus the fluorescence emission 110on an inlet of the fiber optic cable 122. The fiber optic cable 122 isconfigured to guide or otherwise pass the focused light from the inletto an outlet. The one or more optical components 108 may use differentor less components than the illustrated components without departingfrom the scope of the disclosure. For example, the lens 120 may focusthe light directly onto the detector 112 without including the fiberoptic cable 122. The lens can include a quartz convex lens, or any otherlens appropriate for the wavelengths being measured.

The detector 112 can detect an intensity of the fluorescence emission110. Examples of detected intensities are described later within thisdisclosure. In some implementations, the detector 112 can include amonochromator 114 coupled to a photomultiplier 116. The monochromator114 spatially disperses the fluorescence emission 110 into spectralcomponents while the photomultiplier acts to amplify the detectedfluorescence emission 110.

In some implementations, the apparatus 100 can include a microprocessor124 and a computer-readable storage medium 126 that can storeinstructions executable by the microprocessor 124. Details on suchprocesses are described later within the specification.

In some aspects of operation, the excitation light source 104 emits thelight beam 106 towards the sample 102. After the beam 106 impacts thesample 102, a reflected light 128 is directed to a beam dump 130 while afluorescent light 110 is emitted towards the detector 112. As the beamimpacts the sample 102, either the sample 102 or the light source 104can be moved, rotated, or adjusted to change the angle of incidence ofthe light beam 106 and the surface of the sample holder 102. The anglecan be recorded along with an intensity of the emitted fluorescent light110. All of the previously described components can be combined into acompact, portable unit that can be used in field operations.

FIGS. 2A-2B illustrate detailed cross-sectional views of the examplelight beam 106 directed toward a surface of the example sample holder102. The sample holder 102 can be a quartz cuvette, a glass samplecontainer, or any other sample container with a flat surface that istransparent to the specified wavelengths of the light beam 106. A beamof light directed toward the surface of the sample holder 102 at ashallow angle, as shown in FIG. 2A, can experience a certain depth ofpenetration into the sample (d1). If the angle is steepened relative tothe surface, as shown in FIG. 2B, then a greater depth of penetration(d2) can occur. Varying depths of penetration can result in varyingdegrees of intensity of the emitted fluorescence emission 110. Byvarying the angle of incidence and recording a change in fluorescentintensity with the detector 112, a plot can be created. Different fluidscan produce different plots such that the different fluids can beidentified. Details of such plots are discussed later within thisdisclosure. In order to vary the angle (and the depth of penetration),at least one of the sample or the light source can be moved (forexample, rotated). For example, the incidence angle of the light beam106 relative to the surface of the sample holder 102 can vary from0°-80°.

FIGS. 3A-3B are perspective detailed views of an example sample holdermount 300. In this example, the sample holder 102 is a rectangular shapeand is supported by a vertical support 302. Sample holder 102 can beconnected to the vertical support by a strap 304 or other types ofattachments. In this example, the sample holder 102 is connected, by itsbase, to a rotation stage 306. As previously mentioned, to change theangle of incidence, the sample holder 102 can be moved, the light source104 can be moved, or both can be moved. The illustrated exampledemonstrated one implementation of adjusting the angle of incidence bymoving the sample holder 102. That is, the rotation stage 306 can beattached to a base of the sample holder 102 and is capable of rotatingthe surface of the sample holder 102 relative to the propagation axis ofthe excitation light. In illustrated implementations, the sample holder102 can be rotated about a central vertical axis 308 a that passesvertically through the center of the sample holder 102. In someimplementations, the sample holder 102 can be rotated about a verticalaxis 308 b off set from the central axis of the sample holder 102. FIGS.4A-4B are top-down views of a sample holder 102 positioned on a rotationstage 306. As illustrated by FIG. 4A, the axis of rotation 308 a of thesample holder 102 can be positioned vertically through the center of thesample holder 102. As illustrated in FIG. 4A, the axis of rotation 308 bof the sample holder 102 can be positioned vertically through the centerof the surface of the sample holder 102.

FIG. 5 is a schematic diagram showing an example implementation in whichthe light source 104 moves in order to adjust the angle of incidencerather than the sample holder 102. That is, a movable mount 502 can beattached to the light source 104. The movable mount 502 can change anincident angle of the excitation light source 104 relative to thesurface of the sample holder 102. This is accomplished by moving theexcitation light source 104 from a first position 504 a to a secondposition 504 b. In some implementations, the beam catcher 130 can movein conjunction with the light source 104 or the sample holder 102.

FIGS. 6A-6D are example plots that can be plotted based upon anintensity of the fluorescent emissions 110 emitted from a sample withinthe sample holder 102 in relation to the incidence angle. In someinstances, the sample can include a hydrocarbon fluid. The testingapparatus can produce plots with either a clear or opaque sample. Once aplot is recorded, it can be compared to a library of known plots todetermine the contents of the sample.

FIG. 7 is a flowchart showing an example method 700 that can be used todetermine a content of a sample. At 702, a sample is received by asample holder that defines an inner cavity configured to hold a sample.The sample holder 102 includes a surface that is transparent to theexcitation light source 104. In some implementations, the sample can bea fluid. At 704, fluorescence is induced in the fluid sample by asingle-wavelength light beam 106 produced by the light source 104. At706, an angle of incidence between the surface of the sample holder andthe light is changed. The angle of incidence can be changed by adjustingan angle and position of the light source 104, an angle of the sampleholder 102, or both. The change in the angle of incidence can varybetween 0°-80°. At 708, a change in fluorescence intensity is detectedby a detector 112 as the angle of incidence is changed. At 710, a plotof fluorescence intensity vs. the angle of incidence is plotted. At 712,the plot is compared to a library of plots. At 714, a content of thesample is determined in response to comparing the plot. In someimplementations, aspects of the method 700 can be at least partiallyexecuted by the microprocessor 124.

Implementations of the subject matter and the operations described inthis disclosure can be implemented in digital electronic circuitry, orin computer software, firmware, or hardware, including the structuresdisclosed in this disclosure and their structural equivalents, or incombinations of one or more of them. Implementations of the subjectmatter described in this disclosure can be implemented as one or morecomputer programs, i.e., one or more modules of computer programinstructions, encoded on computer storage medium for execution by, or tocontrol the operation of, data processing apparatus. Alternatively, orin addition, the program instructions can be encoded on anartificially-generated propagated signal, such as, a machine-generatedelectrical, optical, or electromagnetic signal, that is generated toencode information for transmission to suitable receiver apparatus forexecution by a data processing apparatus. A computer storage medium canbe, or be included in, a computer-readable storage device, acomputer-readable storage substrate, a random or serial access memoryarray or device, or a combination of one or more of them. Moreover,while a computer storage medium is not a propagated signal, a computerstorage medium can be a source or destination of computer programinstructions encoded in an artificially-generated propagated signal. Thecomputer storage medium can also be, or be included in, one or moreseparate physical components or media (such as, multiple CDs, disks, orother storage devices).

The operations described in this disclosure can be implemented asoperations performed by a data processing apparatus on data stored onone or more computer-readable storage devices or received from othersources.

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, a system on a chip, or multipleones, or combinations, of the foregoing. The apparatus can includespecial purpose logic circuitry, such as, an FPGA (field programmablegate array) or an ASIC (application-specific integrated circuit). Theapparatus can also include, in addition to hardware, code that createsan execution environment for the computer program in question, such as,code that constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, a cross-platform runtimeenvironment, a virtual machine, or a combination of one or more of them.The apparatus and execution environment can realize various differentcomputing model infrastructures, such as web services, distributedcomputing and grid computing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, object, orother unit suitable for use in a computing environment. A computerprogram may, but need not, correspond to a file in a file system. Aprogram can be stored in a portion of a file that holds other programsor data (such as, one or more scripts stored in a markup languagedocument), in a single file dedicated to the program in question, or inmultiple coordinated files (such as, files that store one or moremodules, sub-programs, or portions of code). A computer program can bedeployed to be executed on one computer or on multiple computers thatare located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this disclosure can beperformed by one or more programmable processors executing one or morecomputer programs to perform actions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, such as, an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for performing actions in accordance with instructions andone or more memory devices for storing instructions and data. Generally,a computer will also include, or be operatively coupled to receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, such as, magnetic, magneto-optical disks, or opticaldisks. However, a computer need not have such devices. Moreover, acomputer can be embedded in another device, such as, a mobile telephone,a personal digital assistant (PDA), a mobile audio or video player, agame console, a Global Positioning System (GPS) receiver, or a portablestorage device (such as, a universal serial bus (USB) flash drive), toname just a few. Devices suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, such as, EPROM, EEPROM, and flash memory devices; magneticdisks, such as, internal hard disks or removable disks; magneto-opticaldisks; and CD-ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, implementations of the subjectmatter described in this disclosure can be implemented on a computerhaving a display device, such as, a CRT (cathode ray tube) or LCD (fluidcrystal display) monitor, for displaying information to the user and akeyboard and a pointing device, such as, a mouse or a trackball, bywhich the user can provide input to the computer. Other kinds of devicescan be used to provide for interaction with a user as well; for example,feedback provided to the user can be any form of sensory feedback, suchas, visual feedback, auditory feedback, or tactile feedback; and inputfrom the user can be received in any form, including acoustic, speech,or tactile input. In addition, a computer can interact with a user bysending documents to and receiving documents from a device that is usedby the user; for example, by sending web pages to a web browser on auser's client device in response to requests received from the webbrowser.

While this disclosure contains many specific implementation details,these should not be construed as limitations on the scope of what may beclaimed, but rather as descriptions of features specific to particularimplementations of particular inventions. Certain features that aredescribed in this disclosure in the context of separate implementationscan also be implemented in combination in a single implementation.Conversely, various features that are described in the context of asingle implementation can also be implemented in multipleimplementations separately or in any suitable sub combination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to a subcombination or variation of a sub combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed to achieve desirableresults. Moreover, the separation of various system components in theimplementations described above should not be understood as requiringsuch separation in all implementations, and it should be understood thatthe described components can generally be integrated together in asingle product or packaged into multiple products.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the followingclaims. In some cases, the actions recited in the claims can beperformed in a different order and still achieve desirable results. Inaddition, the processes depicted in the accompanying figures do notnecessarily require the particular order shown, or sequential order, toachieve desirable results.

What is claimed is:
 1. A method comprising: receiving a fluid sample bya sample holder defining an inner cavity configured to hold a sample andincluding a surface transparent to an excitation light source; inducingfluorescence in the fluid sample by a light produced by asingle-wavelength light source; changing an angle of incidence betweenthe surface of the sample holder and the light; and detecting a changein fluorescence intensity by a detector as the angle of incidence ischanged.
 2. The method of claim 1, further comprising: plotting a plotof fluorescence intensity vs. the angle of incidence; comparing the plotto a library of plots; and determining a content of the fluid sample inresponse to comparing the plot.
 3. The method of claim 1, whereinchanging the angle of incidence comprises rotating the sample holder. 4.The method of claim 3, wherein rotating the sample holder comprisesrotating the sample holder about an axis of rotation of the sampleholder that is positioned vertically through the center of the sampleholder.
 5. The method of claim 3, wherein rotating the sample holdercomprises rotating the sample holder about an axis of rotation of thesample holder that is positioned vertically through the center of a faceof the sample holder.
 6. The method of claim 1, wherein changing anangle of incidence is controlled by a microprocessor.
 7. The method ofclaim 1, wherein the fluid sample comprises hydrocarbon fluid.
 8. Themethod of claim 1, wherein changing the angle of incidence comprisesvarying the angle between 0°-80°.
 9. A fluid identification systemcomprising: a sample holder filled with an unknown fluid, the sampleholder being transparent to a specified wavelength of light; a laserconfigured to direct a laser beam towards a face of the sample holder; adetector directed towards the face of the sample holder, the detectorconfigured to detect florescent emissions from the unknown fluid withinthe sample holder; a microprocessor; and a computer-readable storagemedium storing instructions executable by the microprocessor, theinstructions comprising; emitting a laser beam from a laser at the faceof the sample holder; inducing fluorescence in the fluid by the laserbeam produced by a laser at a specified wavelength; changing an angle ofincidence between the face of the sample holder and the laser beam;detecting a change in fluorescence intensity as the angle of incidenceis changed; plotting a plot of fluorescence intensity vs. the angle ofincidence; comparing the plot to a library of plots; and determining acomposition of the fluid in response to comparing the plot.
 10. Thefluid identification system of claim 9, wherein the unknown fluidcomprises a hydrocarbon fluid.
 11. The fluid identification system ofclaim 9, wherein rotating the sample holder comprises rotating thesample holder about an axis of rotation of the sample holder that ispositioned vertically through the center of the sample holder.
 12. Thefluid identification system of claim 9, wherein rotating the sampleholder comprises rotating the sample holder about an axis of rotation ofthe sample holder that is positioned vertically through the center of asurface of the sample holder.